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FAQs on the Ongoing Gulf of Mexico Dolphin Die-off

What processes are under way to examine the potential effects of the Deepwater Horizon BP (DWHBP) oil spill on marine mammals?

There are multiple processes under way that are investigating the potential effects of the Deepwater Horizon BP (DWHBP) oil spill on marine mammals.

Given the overall complexity of the UME investigation and its overlap with and potential importance to ongoing legal investigations, all of the different investigative teams are coordinating their activities. This coordination ensures that all data and samples are collected, preserved, and stored appropriately, legally, and using the best scientific methods and are analyzed with the best available scientific tools so that they are useful to all parties interested in the health of marine mammals in the Gulf of Mexico.

What is an Unusual Mortality Event (UME)?

An Unusual Mortality Event (UME) is defined under the Marine Mammal Protection Act as a stranding that is unexpected, involves a significant die-off of any marine mammal population, and demands immediate response. There are seven criteria used to determine whether a mortality event is "unusual." If the Working Group on Marine Mammal Unusual Mortality Events (WGMMUME), a group of marine mammal health experts, determines that an event meets one or more of the criteria, then an official UME is declared.

How many UMEs have previously occurred in the Gulf of Mexico?

19 UMEs have occurred in the Gulf of Mexico (12 of which involved cetaceans; the remaining 7 were specific to manatees only) since 1991, when the marine mammal UME program was established. More information on UMEs is available on our website.

What are the causes of previous UMEs in the Gulf and what is the cause of the current UME?

Are there any preliminary results available at this time for the current UME?

Current results available from the UME investigation can be found here.  NOAA will make every effort to make new data available to the public as soon as it is legally and scientifically appropriate and possible.

How many dolphins have stranded in the UME?

Please see the weekly updates on the Northern Gulf of Mexico UME website. Please note the numbers listed are preliminary and may be subject to change.

Since not all cetaceans that have died will wash ashore and be found, the number reported stranded is likely a fraction of the total number of cetaceans that have died during the UME.

What role does Brucella play in the UME?


What age classes of dolphins have been impacted?

In general, throughout the region, strandings have been high for all age classes of dolphins. While it is typical to see a peak in strandings of premature, stillborn, and neonatal dolphins (<115cm) in the spring in the northern Gulf of Mexico, the peak observed in 2011, particularly in Mississippi and Alabama, was higher than expected. 

What are the goals of the UME investigation?

There are four goals of any UME investigation, to:

NMFS and our Marine Mammal Stranding Network partners have been working throughout this event to collect samples using consistent protocols, archive and preserve samples using chain of custody protocols, and have submitted appropriate samples, as needed, to laboratories.

Have samples collected from marine mammals been analyzed already?

Throughout the oil spill response and UME investigation, some samples were held at the facilities where they were collected, some were shipped for analyses, and others were shipped to be archived until information gained in the investigation indicates that further analyses are needed.

To date, some samples have been submitted for analysis, including:

Where are the rest of the samples?

Data, record, and sample inventories are being catalogued following chain of custody at each Stranding Network facility, and samples are being shipped to either laboratories for analyses or to the National Marine Mammal Tissue Bank for archiving until such analyses are needed in the investigation. Original data records and photographs are being shipped to the NMFS Laboratory in Miami for review and archiving.

Due to the destructive processes used during chemical analyses, samples may be archived while methods are developed and/or decisions are made by the UME investigative team on those tissues and those methods needed.

Given the state of decomposition of many of the carcasses, initial evaluations of the viability of the samples for specific analyses is being done before they are submitted for chemical or some biological analyses. Sample shipment to laboratories will continue as new carcasses come in.

When will these marine mammal samples be analyzed?

The investigative team is taking a tiered approach relying on pathology and epidemiology to guide the direction additional analyses may need to go as we rule in or out physical, chemical or biological factors that may be contributing to or causing these mortalities.

Many of the carcasses have been moderately to severely decomposed, which significantly reduces the ability to perform many analyses. Some sample analyses are not possible given the decomposition of the carcasses.

Is NMFS/NOAA also evaluating live marine mammals in the northern Gulf?

It is crucial that the UME investigative team evaluates what is going on with live cetaceans in areas where elevated strandings have occurred. As such, the UME investigation benefits from ongoing NRDA studies on live animals in coastal areas of the northern Gulf.

What other studies are going on to assess the effects of the Deepwater Horizon BP oil spill on marine mammals?

Shortly after the oil spill response was initiated, the NRDA process for marine mammals began (early May 2010). Under the NRDA, a variety of studies are being conducted to try to determine potential impacts from the spill on marine mammals. These studies have focused on understanding the type, severity, magnitude, and duration of exposure of oceanic, coastal, and estuarine marine mammals to oil. 

One study found a high prevalence of lung disease and evidence of hypoadrenocorticism (low functioning of the adrenal gland which altered stress response) in live bottlenose dolphins in Barataria Bay, Louisiana. These abnormalities are consistent with adverse health effects previously documented in mammals following oil exposure. 

These studies are ongoing and will likely continue for some time until we understand what impacts may have occurred. Additional information on NRDA marine mammal studies can be found here: 


Where can I find additional information on UMEs?

Updated: February 12, 2015